Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
  • G02F1/125—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves in an optical waveguide structure
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
  • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure

Definitions

• the invention relates to integrated optics and more specifically relates to an optical tunable filter. It can be used as a tunable filter for frequency compression of signals in fiber-optic communication systems, a small-sized tunable optical spectrometer, or a filter element in the equipment for reading data from fiber Bragg sensors.
• a device is known - an integrated multi-reflective tunable filter (A. V. Tsarev, "Tunable optical filters", United States Patent No. 6,999,639, February 14, 2006, Published on February 14, 2006, Foreign Application Priority Data Sep 06, 2001; AB Tsarev, “Multiplexers for WDM with nanophotonic reflectors - a new way to control many hundreds of optical spectral channels”, Nano and Microsystem Engineering, N ° 4, pp. 51-55 (2007)), containing channel optical waveguides for optical input / output radiation and propagation of a light beam, light beam dividers arranged in series along radiation in the form of inclined elementary reflectors; a set of connecting channel optical waveguides for transmitting optical radiation reflected from opposite elementary reflectors.
• A. V. Tsarev integrated multi-reflective tunable filter
• the filtering of a given wavelength of the optical spectrum is carried out due to the constructive interference of many optical beams reflected from the inclined elementary reflectors, periodically located along the channel optical waveguides.
• Tuning of the filtered wavelength of light is carried out due to a controlled change in the refractive index in phase-shifting optical elements located along waveguides containing inclined reflectors (for fine tuning) and a set of connecting waveguides (for wide tuning).
• Their task is to form a constant phase shift between any two optical beams reflected from neighboring elementary reflectors.
• the level of the side lobes in the passband of the filter can be reduced to a level greater than -20 dB due to apodization, by changing the beam division coefficient when reflected from elementary reflectors.
• a similar type of filter is known (using a plurality of inclined reflectors), which operates on the basis of the interference of a plurality of beams propagating in a planar optical waveguide, which provide the possibility of wide wavelength tuning due to the acousto-optical (AO) effect
• A.V. Tsarev. Acoustic-optical tunable filter
• patent of the Russian Federation X ° 2182347, May 10, 2002, published in Bul. 13, dated May 10, 2002 AVTsarev " Acousto-optical variable filter ", United States Patent No. 7,092,139, Published on August 15, 2006, Foreign Application Priority Data August 04, 2000).
• light beam dividers in the form of periodically arranged oblique elementary reflectors that intersect the core of the channel waveguide are made in such a way that the reflected beams propagate further along the planar waveguide, and then again arrive at a similar channel waveguide with many inclined reflectors, which is called filtering an element.
• the filtering of a given wavelength of the optical spectrum is also carried out due to the constructive interference of many optical beams coming from a planar waveguide to inclined elementary reflectors, and which direct optical radiation along the axis of the channel optical waveguide of the filter element.
• there is an optimal angle of the incident beam for which constructive interference works and effective filtering is performed.
• the wavelength can be tuned not only by changing the refractive index of the corresponding channel waveguides (as in the optical filter described above), but also by rotating the phase front during acousto-optical interaction.
• the optical beams that propagate along a planar waveguide interact with a surface acoustic wave (SAW) excited by an on-board transducer (IDT).
• SAW surface acoustic wave
• IDT on-board transducer
• the diffracted optical beam deviates from the incident beam by a double Bragg angle and enters the filter element. In this device, this angle is determined by the length of the acoustic wave, which is controlled by the frequency of the high-frequency signal (hundreds of megahertz) attached to the interdigital transducer.
• Optical coupling of a ring resonator with channel optical waveguides carrying out input / output of optical radiation is carried out due to the tunnel coupling of the wave data s with a ring resonator waveguide
• These filters can be made on various waveguide structures, for example, based on silicon nitride, polymers, lithium niobate or silicon-on-insulator (SOI) structures.
• SOI silicon-on-insulator
• FSR-free spectral range determines the operating range of the filter.
• the wavelength tuning of such ring resonators is carried out due to phase-shifting optical elements operating on the basis of the thermo-optical effect, the electro-optical effect, or a change in the concentration of free charge carriers in the waveguide region.
• the disadvantage of these filters is the low wavelength tuning range, which is proportional to the magnitude of the change in the refractive index, limited by the physical properties of the waveguide material. To expand the tuning range, sometimes use the Vernier effect, i.e.
• filtering is carried out by a consistent change in the refractive index simultaneously for two ring resonators having a narrower and different free spectral band (J. Floriot, F. Lemarchand, and M. Lequime. Tunable double-cavity solid-spaced bandpass filter, Opt. Express, 2004 , v. 12, p. 6289-6298).
• the disadvantage of this type of filter is the difficulty of controlling the wavelength, as well as the presence of spurious signals at wavelengths that are multiples of the free spectral zone of each filter.
• An optical filter is also known (K. Yamada, T. Shoji, T. Tsuchizawa, T. Watanabe, J. Takahashi, and S. Itabashi, "Silicon-wire-based ultrasmall lattice filters with wide freespectral ranges, "Opt. Lett. 28, 1663-1664 (2003)), based on the use of the Mach-Zehnder (MZ) line of interferometers and tunnel coupling of channel waveguides.
• MZ Mach-Zehnder
• the filter is fabricated in SOI structures using complementary metal -second-semiconductor (CMOS) compatible technology (complementary metal-oxide-semiconductor technology (CMOS)) and has a constant difference in the optical length (path-length difference) of different arms of the interferometer (to provide filtering) and a different amount of tunnel coupling (to ensure apodization needed to lower the level of side sculpts tkov).
• CMOS complementary metal -second-semiconductor
• CMOS complementary metal-oxide-semiconductor technology
• these filters are not intended for broadband tuning wavelength, so they are preferred for use as the fixed filter devices with a small number of frequency channels (i.e., with a small set of operating wavelengths).
• the basis of the invention is the task of creating an optical tunable filter that would simultaneously have a wide tuning range and a narrow width of the filtration line, and which could be made on the basis of existing and promising technologies.
• the problem is solved in that in an optical tunable filter containing channel optical waveguides for input-output of optical radiation and propagation of the light beam, light beam dividers arranged in series along the radiation, a means of formation for transmitting optical radiation branched by beam dividers, wherein the forming means is made in the form of a set of connecting channel optical waveguides and / or a planar optical waveguide, according to the invention, divide whether the beam is made in the form of a set of coupled optical waveguides, the mutual arrangement of which is selected taking into account the maintenance at the working wavelength of the radiation of a phase difference essentially multiple of 2 ⁇ for most beams branched out using various beam dividers and passed from the input to the output of the optical filter.
• ⁇ 3.14159 ... is a universal constant.
• the requirement that most beams have a phase difference shift that is essentially a multiple of 2 ⁇ leads to the fact that at the working wavelength all of these beams will fold in phase and form an intense signal at the output of the device. That relatively small number of beams, where this condition is violated, will not make a significant contribution to the signal intensity at the working wavelength. However, their contribution can be useful for the formation of the desired spectral shape characteristics (for example, to suppress spurious signals outside the width of the filter line).
• the device is based on channel and / or plenary waveguides.
• the channel optical waveguide has an increased value of the refractive index both in depth and across the structure, i.e. it is a local region on / or below the surface of a solid in the form of a thin strip with a width of fractions to units of microns, with a refractive index higher than the refractive index of its surroundings.
• the region with an increased value of the refractive index can be both homogeneous and inhomogeneous (the case of a gradient optical waveguide).
• a channel optical waveguide can support low-loss propagation of a narrow and non-diverging optical beam along its axis in the vicinity of a region with an increased refractive index.
• the number of guided (waveguide) waves (modes) that this structure supports, and the spatial distribution of their optical fields are determined by the profile of the change in the refractive index in depth and width.
• a planar waveguide is a thin layer with a thickness of fractions to several microns with a refractive index higher than the refractive index of the surrounding medium (substrate and surrounding upper layer, in this case, air).
• a light beam can propagate inside this layer with very low losses (less than 1 dB / cm).
• Planar waveguides can be either homogeneous or gradient.
• Channel and planar waveguides can be made by diffusion of metals, proton exchange from molten salts, sputtering of materials with a higher refractive index than that of the substrate, epitaxy from the gas or liquid phase, modification of the properties of the surface layer due to irradiation, for example, by electrons and / or photons, etc.
• a channel waveguide can be made by etching grooves on the surface of a planar waveguide.
• the depth of the grooves may partially overlap the core planar waveguide and form a comb-type channel waveguide, or completely cross its core, thereby forming a strip optical waveguide.
• Such waveguides are most promising for creating this type of device in silicon-on-insulator and lithium niobate structures.
• polysilicon As materials for the manufacture of optical waveguides, one can use polysilicon, a mixture (in the required ratio) of silicon oxide (Si0 2 ) and titanium oxide (Ti0 2 , Titanium dioxide), chalcogenide glass (As 2 S 3 ), aluminum nitride (A1N, Aluminum nitride), silicon nitride (Si 3 N 4 , Silicon nitride), silicon oxynitride (SiON, Silicon oxynitride), gallium nitride (GaN, Gallium nitride), polymers and other materials widely used in photonics and integrated optics.
• silicon oxide Si0 2
• Ti0 2 Titanium dioxide
• chalcogenide glass As materials for the manufacture of optical waveguides, one can use polysilicon, a mixture (in the required ratio) of silicon oxide (Si0 2 ) and titanium oxide (Ti0 2 , Titanium dioxide), chalcogenide glass (As 2 S 3 ), aluminum n
• a channel waveguide with corresponding beam dividers through which optical radiation is introduced will be called a forming element
• a channel waveguide with corresponding beam dividers through which optical radiation is output will be called a filtering element.
• Coupled optical waveguides is understood to mean a situation generally accepted in the scientific literature when the energy of an optical wave can flow (partially or completely) between two (or more) optical waveguides due to the tunnel coupling of their optical fields through the space separating them.
• phase-shifting optical elements is understood to mean a situation generally accepted in the scientific literature when the phase of an optical wave propagating through an optical waveguide is controlled by an external signal, for example, due to electro-optical or thermo-optical effects, or the effect of electrostriction, or a change in the concentration of free charge carriers, or under other physical effects (deformation, radiation, etc.).
• the beam expanders can be made in the form of adiabatic horn elements and / or tapering channel waveguides.
• the waveguides of the forming and filtering elements run parallel to each other.
• the connecting waveguides are made normally (at right angles) to the specified waveguides.
• Such a filter design will be called rectangular (orthogonal).
• the waveguides of the forming and filtering elements it is advisable to increase the steepness of the tuning of the wavelength and / or expansion of the free spectral zone, the waveguides of the forming and filtering elements to perform at an angle to each other.
• the connecting waveguides as a rule, are made obliquely to the specified waveguides at an angle different from the straight line. This design of the filter will be called inclined.
• At least one set of control electrodes in the form of strips of conductive material in order to create when the electric field is applied local changes in the refractive index in the vicinity of these waveguides due to electro-optical or thermo-optical effects, or the effect of electrostriction, or a change in the concentration of free charge carriers.
• control electrodes in the form of strips of conductive material in order to create an electric field when applying an electric field to adjust the wavelength of the filtered radiation at the same time of all optical channels and to expand the range of the tuning of wavelengths of light of an optical filter, in the immediate vicinity of a set of connecting channel optical waveguides local changes in the refractive index in the vicinity of these waveguides due to electro-optical or thermo-optical effects or the effect of electrostriction, or a change in the concentration of free charge carriers, the length of the control electrodes and the magnitude of the voltage applied to them being chosen so as to have the same or different by an even number of ⁇ phase shift for adjacent beams branched by different beam dividers and passed from input to output optical filter.
• the through function in order to ensure the through passage of the broadband optical signal (the through function), it is necessary to place a similar set of electrode structures in the section between the last and the last but one filtering element, the length of the electrodes and the magnitude of the applied voltage to each of the electrodes being chosen so that they have zero or a phase shift differing by an even number ⁇ for adjacent beams branched by different beam dividers and passed from the input to the output of the optical filter.
• the through-passage of the broadband optical signal is carried out for all wavelengths, except those that were rejected by the acousto-optical wave.
• Part of the deflected light beams, at given wavelengths, will be filtered using one or more filter elements. However, it is desirable that all remaining (unfiltered) wavelengths be able to pass through the device through.
• an optical filter with at least one additional source of acoustic waves, configured to generate an acoustic wave directed against the acoustic wave of the main source and capable of interacting with the light waves of the beam in the area between the last and penultimate filtering elements.
• both the shape of the transmission line and its envelope in the spectral range of the filter can be adjusted. For example, to ensure significant suppression (more than 20 dB) of the side lobes, it is advisable to perform beam dividers with different fission factors. This is ensured by changing the magnitude of the tunnel coupling, which is selected so as to provide the optimal amplitude of the beams and / or phase of the waves branched by various beam dividers. At the same time, at the output of the device, the contribution to the resulting signal from different beams, as a rule, decreases from the middle part of the forming and filtering elements to their ends.
• apodization is understood as the case generally accepted in the scientific and technical literature when the amplitudes and / or phases of various signal components vary, the summation of which forms the spectral response of the device. Therefore, apodization can be amplitude, phase, or mixed (amplitude-phase). Most interference optical devices use apodization to improve their specifications.
• beam dividers and / or channel waveguides of the forming and / or filtering elements and / or connecting waveguides can be made in one layer.
• beam dividers and / or channel waveguides of the forming and / or filter elements, and / or connecting waveguides and / or planar waveguides can be made in different layers.
• damping regions can be parts of a structure with a high concentration of free charge carriers, and / or containing scattering centers, and / or submicron diffraction gratings, and / or narrowing (wedge-shaped) channel waveguides with a gradually decreasing core cross section (so that the radiation passing through them increases its spatial size (expanded) and left the area of the optical filter).
• beam dividers and / or channel waveguides of the forming and / or filtering elements and / or connecting waveguides are made in silicon-on-insulator structures.
• the device is made in waveguide structures based on lithium niobate.
• the channel waveguides forming the beam dividers have the same or close effective refractive indices.
• optical filters may contain many intersections of channel waveguides of the forming and / or filtering elements with connecting waveguides. To reduce spurious signals, it is advisable intersect the specified channel waveguides with minimal scattering losses, for example, due to the multilayer intersection method described in the scientific literature using vertical coupling, for example, on the basis of narrowing channel waveguides (see, for example, K.Watanabe, Y. Hashizume, Y. Nasu , Y. Sakamaki, M. Kohtoku, M. Itoh, and Y. Inoue, "Low-loss three-dimensional waveguide crossings using adiabatic interlayer coupling," Electron. Letters 44, 1356-1357 (2008); R. Sun, M .
• Figure 1 depicts a schematic diagram of a single-channel optical filter on coupled waveguides (orthogonal orientation), according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 7-12 are coupled channel optical waveguides of beam dividers of the forming element, 13-18 are coupled channel optical waveguides of beam dividers of the filtering element, 30-32 - curved channel optical waveguides, 36-41 - connecting channel optical waveguides, 60 - tapering channel optical waveguide, 61 - input of the optical filter, 62 - output of the optical filter for the first spectrally channel, 66 — output of an optical filter for monitoring input radiation, 70 — optical beams branched by beam dividers.
• Figure 2 depicts a schematic diagram of an optical single-channel filter on coupled waveguides (orthogonal orientation, the case of intersection with connecting waveguides), according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 7-12 are coupled channel optical waveguides of beam dividers of the forming element, 13-18 are coupled channel optical waveguides of beam dividers of the filtering element, 30-32 - curved channel optical waveguides, 36-41 - connecting channel optical waveguides, 60 - tapering channel optical waveguide, 61 - input optical filter, 62 — output of the optical filter for the first spectral channel, 66 — output of the optical filter to control the input radiation, 70 — optical beams branched by beam dividers.
• Fig. 3 depicts a schematic diagram of a single-channel optical filter on coupled waveguides (oblique orientation), according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 7-12 are coupled channel optical waveguides of beam dividers of the forming element, 13-18 are coupled channel optical waveguides of beam dividers of the filtering element, 30-32 - curved channel optical waveguides, 36-41 - connecting channel optical waveguides, 60 - tapering channel optical waveguide, 61 - input of the optical filter, 62 - output of the optical filter for the first spectrally channel, 66 — output of the optical filter to control the input radiation, 70 — optical beams branched by beam dividers, ⁇ — orientation angle of the waveguides of the forming and filtering elements, measured relative to the normal to the connecting waveguides.
• Figure 4 depicts a schematic diagram of a two-channel optical filter on coupled waveguides, according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 and 4 are channel optical waveguides of the filtering elements, 7-12 are coupled channel optical waveguides of the beam dividers of the forming element, 13-18 and 19-24 are coupled channel optical waveguides of the filtering beam elements, 30-32 - curved channel optical waveguides, 36-41 - connecting channel optical waveguides, 60 - tapering channel optical waveguide, 61 - input of the optical filter, 62 and 63 - output of the optical filter for the first and the second spectral channels, 66 — output of the optical filter for monitoring the input radiation, 70 — optical beams branched by beam dividers.
• Figure 5 depicts a schematic diagram of a single-channel optical filter-multiplexer on coupled waveguides, according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 and 6 are channel optical waveguides of the filtering elements, 7-12 are coupled channel optical waveguides of the beam dividers of the forming element, 13-18 are coupled channel optical waveguides of the beam dividers of the filtering element, 71- 76 coupled channel optical waveguides of filter beam dividers element for the transmission function, 30-32 - curved channel optical waveguides, 36-41 - connecting channel optical waveguides, 60 - tapering channel optical waveguide, 61 - input of the optical filter, 62 - output of the optical filter for the first spectral channel, 65 - output of the optical filter for the transmission function, 66 — output of the optical filter for monitoring the input radiation, 70 — optical beams branched by beam dividers.
• FIG. 6 depicts a schematic diagram of a three-channel optical filter-multiplexer on coupled waveguides, according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3-6 are channel optical waveguides of the filtering elements, 7-12 are coupled channel optical waveguides of beam dividers of the forming element, 13-18, 19-23, 54-58 are coupled channel optical waveguides of beam dividers of filter elements of different spectral channels, 71-76 coupled channel optical waveguides of beam dividers of filter element for transmission function, 30-32 - curved channel optical waveguides, 36-41, 44-48, 49-53, 54-58 connecting to anal optical waveguides, 60 — tapering channel optical waveguide, 61 — input of the optical filter, 62–64 — outputs of the optical filter for different spectral channels, 65 — output of the optical filter for transmission function, 66 — output of the optical filter to control input radiation, 67- 69
• FIG. 7 depicts a schematic diagram of a single-channel optical filter on coupled waveguides (orthogonal orientation with thermo-optical control), according to the invention, where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 7-12 are connected channel optical waveguides of beam dividers of the forming element, 13-18 connected channel optical waveguides of beam dividers of the filtering element, 36-41 - connecting channel optical wave s, 60 — tapering channel optical waveguide, 61 — input of the optical filter, 62 — output of the optical filter for the first spectral channel, 66 — output of the optical filter to control the input radiation, 101-106 — electrodes for heating thermo-optical phase-shifting elements of wide tuning, 107 and 108 - a set of electrode structures with a constant length, 109 and ON - a set of electrode structures with a linearly variable length, 1 1 1-1 12 - electrodes for heating thermo
• Fig. 8. depicts a schematic diagram of a single-channel optical filter with acousto-optic control on coupled waveguides (with adiabatic expansion of horn-type channel waveguides), according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 13-18 are coupled channel optical waveguides of beam dividers of the filtering element, 30-32 are curved channel optical waveguides, 59 is a planar optical waveguide of the forming element , 60 — tapering channel optical waveguide, 61 — input of the optical filter, 62 — output of the optical filter for the first spectral channel, 76 — optical beams branched by beam dividers, 77 — optical beams and rejected by a surfactant, 79 - absorber surfactant 80 - adiabatic expander channel waveguide horn type, 82 - surfactant 83 - interdigital trans
• Fig.9 depicts a schematic diagram of a single-channel optical filter with acousto-optical control on coupled waveguides (two-layer version with adiabatic expansion of the optical beam based on a narrowing channel waveguide), according to the invention, isometry; where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 13-18 are coupled channel optical waveguides of beam dividers of the filtering element, 30-32 are curved channel optical waveguides, 59 is a planar optical waveguide of the forming element , 60 — tapering channel optical waveguide, 61 — input of the optical filter, 62 — output of the optical filter for the first spectral channel, 76 — optical beams branched by beam dividers, 77 — optical beams and, rejected by the SAW, 77 — optical beams passing through the filter element, 79 — SAW absorber, 81 — adiabatic optical beam
• Figure 10 depicts a schematic diagram of a simulation of a single-channel optical filter on coupled waveguides (orthogonal orientation with thermo-optical control), where 1 is a solid-state substrate, 2 is a channel optical waveguide of the forming element, 3 is a channel optical waveguide of the filtering element, 7-12 are coupled channel optical waveguides of beam dividers of the forming element, 13-18 are coupled channel optical waveguides of beam forming of the filter element, 30-32 - curved channel optical waveguides, 36-41 - connecting channel optical waveguides, 61 - input of the optical filter, 62 - output of the optical filter for the first spectral channel, 66 - output d optical filter to control the input radiation, 70 - optical beams branched by beam dividers, 91-95 - FDTD monitors, 97 - damping region, d - gap width of the slit, R - radius of curvature of curved waveguides, LL - length of phase-shifting optical elements
• Figure 1 1 - change in the beam division coefficient for deflected (R c ) and transmitted (T c ) waves, as a function of the distance d between the strip waveguides based on silicon nanowires (calculation 2D FDTD). For comparison, the exponential approximation for R c (d) is given.
• Fig. 12 is an example of the apodization function A p and the beam division coefficients R c and gap gap d between the strip waveguides based on silicon nanowires, as a function of the beam splitter number M (calculation 2D FDTD), necessary for its implementation.
• Fig. 13 is a numerical demonstration of the operation of an optical filter having 32 beam dividers based on silicon nanowires (2D FDTD calculation), where 2 is a channel optical waveguide of a forming element, 3 is a channel optical waveguide of a filtering element, 61 is an input of an optical filter, 62 is an output optical filter, 91, 91, 95 - FDTD monitors.
• the first value indicates the value of ⁇
• the subsequent figures indicate the values of ⁇ , ⁇ 2 and ⁇ 3 in shares of ⁇ 00.
• Fig. 15 shows the beam dividing coefficients R as a function of their M number for different filter elements, which are necessary for creating a narrow-band optical filter multiplexer with a 25 GHz frequency grid; here R ⁇ , R c3 , Rc 6 are the beam division coefficients for different waveguides 2, 3-5, and 6, respectively.
• Fig. 17 shows the beam dividing coefficients R as a function of their number M for different filter elements (case of an acousto-optical filter with a frequency grid of 25 GHz); here, Rc2 and Rc3 are the beam fission factors for different waveguides 2 and 3, respectively.
• AO filter case with a grid of frequencies of 25 GHz and 250 GHz.
• d ⁇ 0 ⁇ m, the optical aperture is 0.58 cm and 0.058 cm, respectively.
• the 25 GHz filter spectra are located inside the 250 GHz filter spectrum;
• Fig. 19 is a spectral dependence of filtering efficiency for an AO filter with a 25 GHz frequency grid.
• d ⁇ 0 ⁇ m, SAW frequency 1225 MHz, optical aperture 0.58 cm.
• the device is as follows. On the surface of the solid-state substrate 1 (Figs. 1–9) or in the immediate vicinity below it (the case of the so-called buried waveguide), channel optical waveguides of the forming (2) and filtering (3-6) elements are made. A set of beam dividers is made on the surface of the solid-state substrate 1 (Figs. 1–9) or below it in the immediate vicinity of the channel optical waveguides (2, 3) of the forming and filtering elements, including adjacent channel optical waveguides (7-29, 71-76 ), which due to tunnel coupling are able to branch part of the energy of the incident beam into these waveguides. The rest of the energy propagates further along the original waveguide to the next similar beam splitter until it reaches the end of the structure.
• the channel waveguides of the beam dividers have curved parts (30-32, 34, 35), which on the one hand serve to smoothly change the coupling coefficient (30-32) to reduce spurious reflection, and on the other hand, make it possible to optimally arrange all the conclusions of the beam dividers for subsequent connection with means of formation.
• the direction of the channel waveguide changes due to the effect of specular reflection from a region with a high reflection coefficient, for example, due to the effect of total internal reflection (FR) at a vertically etched border.
• the forming means comprises a set of curved (34, 35) and direct (36-41, 44-58) channel waveguides, and / or a planar waveguide (59).
• a planar waveguide 59 is made on the surface of the solid-state substrate 1 (see Fig. 8 and Fig. 9) or under it in close proximity to the waveguides of the forming 2 and filtering 3 elements, which is optically matched with the indicated strip waveguides (to reduce spurious scattering )
• a horn expansion of the beam see Fig. 8 and / or an adiabatically tapering waveguide 81 (see Fig. 9) were made.
• the latter is usually performed on the upper layer of the multilayer structure and ensures the expansion of the beam and the transition of the optical wave between two waveguide layers (from a channel waveguide to a planar waveguide).
• This optical element operates on the well-known principle that the optical field of a guided wave (fundamental waveguide mode) adiabatically increases in size as the wave propagates to the narrow end (VR Almeida, RR Panepucci, and M. Lipson, "Nanotaper for compact mode conversion,” Opt. Lett. 28, 1302-1304 (2003)).
• the channel optical waveguide 2 is an integral part of the forming element, and through its input 61 an optical beam is introduced into the filter, which may contain different wavelengths of the optical spectrum.
• the input of light into the channel optical waveguide 2 can be carried out in various ways, for example, by docking with a fiber optical fiber, focusing the optical radiation on the end of the structure, using an I / O grating element, etc.
• channel optical waveguides 3-6 are an integral part of the filter element, and through their outputs 62-65 output optical beams that have passed through the forming means.
• channel waveguides of beam dividers 7-29, 71-76 are made, which are tunnel connected with these waveguides 2-6.
• Coefficient of division of beam energy into coupled waveguides depends on the length of the communication region (usually increases with its increase), on the overlap of the mode fields of each of the waveguides (usually decreases with increasing distance between the waveguides) and the magnitude of the phase mismatch of their fields (depends on the effective refractive indices of the modes of the respective waveguides).
• the beam splitter may contain more than two waveguides, for example, three channel waveguides (see (Doo Gun Kim, Jae Hyuk Shin, Cem Ozturk, Jong Chang Yi, Youngchul Chung, Nadir Dagli, "Rectangular Ring Lasers Based on Total Reflection Mirrors and Three Waveguide Couplers," Photonics Technology Letters, IEEE, vol.19, no.5, pp.306-308, (2007)). It is important that the coefficient fission varies widely (from 0 to 1) by changing the parameters of the coupling element of the optical waveguides, which performs the function of a beam splitter. 1 to 9, the channel waveguides of the beam dividers 7-29, 71-76 are made at different distances from the waveguides 2-6, which provides the necessary apodization.
• phase-shifting optical elements are used that operate on the basis of electro-optical or thermo-optical effects, the effect of electrostriction, or changes in the concentration of free charge carriers.
• the technology for the manufacture of electrodes and the design of phase-shifting optical elements are described in detail in the scientific and technical literature.
• Fig.7 presents embodiments of the device based on the thermo-optical effect.
• electrode structures 101-1 12 are made on the surface of the structure, the heating of which during the flow of electric current causes local changes in the refractive index in the region of the optical waveguide.
• the electrodes 101-106 are controlled independently of multi-channel direct or alternating current sources (not shown) or are grouped, for example, with a period of 4 (i.e., each 4 is powered in parallel) to reduce the number of channels at the current source.
• groups of electrodes 107-108 and 109-1 10 are made sequentially along the path of optical radiation, moreover, electrodes 107-108 are made with p constant electrode length, and group 109-1 10 has a ramp length from the number of the connecting channel waveguide on which they are made. Heating of the electrodes 109-1 10 gives a linear phase change within each group. Heating of the electrodes 107-108 provides a linear phase change (accurate to a constant bias of 2 ⁇ ) throughout the filter structure.
• the electrodes 1 1 1 and 1 12 are made along the optical waveguides forming 2 and filtering 3 elements.
• strip 2 and 3 as well as planar 59 waveguides are made.
• at least one electrode structure of the interdigital transducers 83 is made, which is powered by a high-frequency radiation source 84.
• adiabatic beam expanders of horn type 80 are made (see Fig. 8) and based on the tapering channel waveguides 81 (see Fig.9).
• an acoustic absorber 79 is made, for example, based on a rubberized compound.
• tapered tapered waveguides 60 are made.
• the device in Fig. 9 is expediently made in two waveguide layers separated by a buffer layer with a low refractive index. Moreover, most of the device is made on the main substrate, and channel waveguides of beam dividers 7-18 are made on the upper layer.
• the operation of the optical filter can be characterized as follows. Having arrived at the input of the device 61 (see Fig. 1-9), the light beam sequentially passes through the beam dividers and enters the forming means in the form of a set of beams (see arrows) with a strictly specified amplitude and phase, which are determined by the parameters of the communication elements of the corresponding channel optical waveguides 2-6 with channel waveguides 7-29, 71-76. Part of the radiation passes through the waveguide 2 to its end 66 and can be used to control the level of the input signal (out function). However, for the optimal design of the device, most of the energy of the input beam is transferred to the means of formation in the form of coherent light beams 70, which provide filtering properties of the device.
• the optical beams come from the forming element to the connecting channel waveguides 36-41 in the form of coherent light beams 70 and then sequentially pass through the beam dividers of the filter element formed by coupled waveguides 3 and 13-18. On each such element, the optical beam is divided into two parts, one passes further along the curved waveguides 32 to the tapering ends 60, which are used as damping elements (to remove unnecessary radiation from the structure). The other part tunnels into waveguide 3 and sequentially passes further through similar beam dividers.
• the optical fields (taking into account their amplitudes and phases) are added to the beam dividers from the side of the corresponding connecting waveguides 36-41, and the fields already entered into waveguide 3 from the previous (along the optical radiation) beam dividers.
• the mutual arrangement of the beam dividers is selected taking into account the maintenance of the phase difference at the working radiation wavelength for most beams branched with different beam dividers, essentially a multiple of 2 ⁇ . Therefore, at the working wavelength, all such beams will be summed in phase and their amplitudes will increase as they propagate along waveguide 3 (see the increase in the width of the arrows, which illustrate the increase in amplitude). For all other wavelengths, the phase incursion for any pair of beams will be arbitrary (not a multiple of 2 ⁇ ) and the condition of constructive interference will be violated, therefore, the intensity that has passed before the output of the 62 optical wave will be small. Thus, this device will perform the function of optical filtering for those wavelengths for which the above condition of multiplicity 2 ⁇ is fulfilled.
• the optical filter can be implemented both in the orthogonal orientation (see Fig. 1 and Fig. 2), and inclined (see Fig. C). Its distinctive feature is that it allows you to increase the steepness of perestroika. wavelengths and / or expand the size of the free spectral zone.
• an angle range of 45 ° ⁇ ⁇ 65 ° is used for oblique orientation.
• the condition of constructive interference at the operating wavelength Lo is described by the expression:
• A is the location step of the connecting waveguides; ⁇ ] and N? - effective refractive indices of the fundamental mode of the channel waveguides of the forming and filtering elements, respectively; N i + i and N, are the effective refractive indices of the fundamental mode of the channel waveguides of two adjacent connecting waveguides (with numbers i + 1 and /); L - the same length connecting waveguides; t is the interference order, which determines the magnitude of the free spectral zone ⁇ of the optical interference filter:
• the basic rules are formulated for controlling the wavelength of the proposed type of optical filter, which can be controlled by changing the refractive index of the channel waveguides of the forming and filtering elements and / or connecting waveguides.
• the refractive index of the channel waveguides of the forming and filtering elements changes simultaneously by 8zier Canalica ⁇ ntzrien. Then, from expression (1), we can find the corresponding change in the working wavelength:
• optical filter control described above can be carried out monotonously along the wavelength using phase-shifting elements located along the waveguides of the forming and filtering elements, which we will call fine tuning elements.
• phase-shifting elements will be called elements of a wide wavelength tuning.
• the combination of elements of fine and wide tuning allows you to rebuild the working length of the filter within the free spectral zone with minimal changes in the refractive index SN and AN L in the corresponding optical waveguides, which is an important advantage of the proposed device. This property will be described in more detail below.
• Figure 4 presents a General view of a two-channel optical filter, in which two filters from figure 2 are combined in a single device. Their work is similar to that of a single-channel filter, however, here the optical beams leaving the filter are not damped by the tapering waveguide 60 (see Fig. 2), but pass on along the corresponding channel waveguides (see arrows) and tunnel-connected with the channel waveguide 4 of the second filter element.
• the phase incursion for any pair of beams branched by two beam dividers will be a multiple of 2 ⁇ , and therefore, all such beams will be summed in phase and increase as they propagate along the waveguide 4 (see the increase in the width of the arrows, which illustrate the increase in amplitude). It is important that the condition of multiplicity 2 ⁇ described above, which determines the operating wavelengths of the first and second filter elements, depends on the phase delays of the optical microbeams from input 61 to outputs 62 and 63, and therefore, the lengths of the filtered waves can be controlled by the method described above by changing the parameters and the location of the corresponding channel waveguides forming the structure of the optical filter.
• Fig. 6 This device implements the function of a three-channel multiplexer. It contains one forming element with an input 61, three filter elements with outputs 62-64, from which optical radiation can be derived at three different wavelengths, as well as a filtering element of the transmission function with terminal 65.
• the operation of the device is as follows.
• An optical beam containing a plurality of optical wavelengths enters the input 61 as they propagate along the channel waveguide 2 and branch into the channel waveguides 7-11 due to the tunnel coupling.
• Each of the branched beams propagates along corresponding channel waveguides and in the course of propagation pass through the communication elements of various filter elements.
• the device is made taking into account maintaining the phase difference at the working wavelengths of the radiation for any pair of beams of each of the filter elements branched out using different beam dividers, essentially a multiple of 2 ⁇ . In this orthogonal design, any optical beams undergo the same phase shift along the path from the beam dividers of the forming and filtering elements.
• the required phase shift (a multiple of 2 ⁇ ) for filtering is mainly due to the optical delay between the respective beam dividers, for example, 7 and 8, as well as 26 and 25 (from input 61 to output 64).
• the required 2 ⁇ phase shift is achieved at different wavelengths, which is determined by the location period of the respective beam dividers, as well as the refractive index of the channel waveguides that form the structure of the optical filter. This allows you to organize tunable filtering of optical radiation at the output 62-64 of the corresponding filter elements using controlled phase-shifting optical elements, as well as the passage to the exit of 65 of all remaining (unfiltered wavelengths).
• signals at optical wavelengths of the corresponding filter elements can be input to pins 67, 68 and 69.
• the subsequent filter element 4 and / or 5 may have the same operating wavelength. This provides better suppression of a given wavelength in the transmitted signal, which reduces the level of spurious interference for optical signals at the same wavelength that can come from input 68 or 69.
• this device can be controlled using phase-shifting optical elements for thin and wide tuning of the wavelength, as illustrated in Fig.7.
• the first of them are located along the channel optical waveguides forming 2 and filtering 3-6 elements (see Fig.6). They change the refractive index and, therefore, the phase delay on the path between adjacent beam reflectors. As a result, the required phase shift (a multiple of 2 ⁇ ) is achieved at wavelengths different for different channels, which depend on a change in the refractive index in the respective waveguides 2-6.
• Phase-shifting elements on waveguides 3-5 allow you to independently change the operating wavelength of each of the filter elements, however, the range of wavelength tuning is limited by the small possible change in the exponent and phase shift at a small distance (usually of the order of 10 ⁇ m) between adjacent beam dividers.
• phase-shifting elements of wide tuning on connecting waveguides are used (36-41, 44-48, 49-53, 54-58). Their length can be large enough, which removes the restriction on the magnitude of the phase shift and, therefore, on the range of wavelength tuning.
• Their task is to create a constant change in the phase shift as the number of the corresponding connecting waveguide increases (36-41, 44-48, 49-53, 54-58).
• phase shift is compensated (due to the detuning of the wavelength) by changing the phase delay in the respective waveguides 2-5.
• Any predetermined working wavelength can be filtered by sharing phase-shifting optical elements for fine and wide tuning of the wavelength.
• the channel optical waveguides 2 and 3 are made in the immediate vicinity of the planar optical waveguide 59 are shown in Fig. 8 and Fig. 9.
• the optical beams branched on beam dividers pass into the planar waveguide 59 using adiabatic beam expanders (80 or 81), which terminate the corresponding coupling elements of the beam dividers.
• a set of coherent optical beams 76 are formed in the planar waveguide, which pass through the region along which the acoustic wave 82 propagates, which is generated by the source 83 of acoustic waves.
• the period of arrangement of the beam dividers is determined by the free zone ⁇ according to expression (4).
• phased interdigital transducers are usually used, which are a comb of electrodes connected to a high-frequency source 84 of a high-frequency alternating electric field.
• Source 83 due to the piezoelectric effect, effectively excites a surface acoustic wave, which propagates in the surface the region occupied by the optical waveguide 59, and can come into effective interaction with guided optical waves.
• the phase fronts of beams formed and guided by adiabatic beam expanders should be located at a Bragg angle ⁇ to the phase front of the acoustic wave:
• L is the SAW wavelength
• L v / F
• v and F are the speed and frequency of the SAW
• N is the effective refractive index of the guided mode of the planar waveguide.
• An acoustic absorber 79 is used to exclude SAW reflection, which can lead to the appearance of spurious signals.
• coherent optical beams 76 satisfy the conditions of Bragg phase matching and diffract to the SAW, as a result of which they change the propagation direction to a double Bragg angle and form coherent beams 77.
• the diffracted optical beams 77 with the help of similar adiabatic beam expanders (80 or 81) get from a planar optical waveguide 59 a filtering optical element, made in the form of a channel optical waveguide 3 and a set of beam dividers on coupled waveguides 13-18, and is output from the device through output 62.
• the spectral characteristics of the optical filter are optimized by the apodization method by using different beam fission factors determined by their coupling coefficients, for example, by changing the relative position (gap) of the channel waveguides 7-18, 2, and 3 (see Fig. 8 and Fig. 9).
• the device in Fig. 8 is proposed to be implemented in a single layer, for example, on waveguides in lithium niobate.
• single-mode planar waveguides are created, for example, due to high-temperature diffusion of titanium, which creates a layer in the surface region (of the order of several microns) with a higher refractive index (by a value of the order of 0.01) with respect to the bulk material.
• the structure of channel waveguides is implemented by deep etching technology through the entire waveguide layer.
• each communication element on the channel waveguides ends on one side with an adiabatically expanding region 80 (horn type) to form a relatively wide (about 10 ⁇ m) optical beam 76, and on the other hand with a narrowing waveguide 60 for outputting unused radiation from the device.
• this device is very similar to the device shown in figure 1. The difference is that in figure 1 wide-range wavelength tuning is carried out by linearly varying the refractive index in channel waveguides 36-41. In this device of FIG. 8, it is proposed to tune the wavelength due to the rotation of the phase front during acousto-optical interaction in the planar optical waveguide 59.
• FIG. 9 The structure of FIG. 9 is proposed to be made in two waveguide layers with a high refractive index (for example, Ti: LiNb03 and Si02: Ti02) separated by a buffer layer with a lower refractive index (for example, from silicon dioxide).
• a high refractive index for example, Ti: LiNb03 and Si02: Ti02
• a buffer layer with a lower refractive index for example, from silicon dioxide.
• the adiabatic expansion of the beam is carried out on the basis of a tapering channel waveguide 81, which simultaneously implements the optical matching function of the channel and planar waveguides.
• the principle of operation of such elements has been well studied in the scientific literature (V. R. Almeida, R. R. Panepucci, and M. Lipson, "Nanotaper for compact mode conversion,” Opt. Lett. 28, 1302-1304 (2003)).
• V. R. Almeida, R. R. Panepucci, and M. Lipson "Nanotaper for compact mode conversion," Opt. Lett. 28, 1302-1304 (2003)).
• the aforementioned tapering channel waveguide 81 converts optical radiation into a downstream channel waveguide, in which it expands to the desired size using the adiabatic region 80 (horn type) due to tunneling. Its task is to form a slightly diverging optical beam, which propagates at a Bragg angle to the front of the acoustic wave in order to ensure effective acousto-optical interaction.
• the relative position of the beam dividers of the devices of Fig. 8 and Fig. 9 are selected taking into account the maintenance of the phase difference at the working radiation wavelength for any pair of beams 76 or 77, essentially a multiple of 2 ⁇ .
• the phase shift for any beams passing from the input 61 to the output 62 is essentially a multiple of 2 ⁇ .
• the working wavelength of light most optical waves develop in phase and the filter will skip the specified wavelength of light.
• the condition of constructive interference is violated, and the transmission of the signal to output 62 will decrease by several orders of magnitude (signal obstruction).
• These beams (at all other wavelengths) are damped (see Fig. 8) or pass further (see Fig.
• the filter can leave the filter or be used for further processing, for example, in the case of several similar filters that perform multichannel filtering (similar to figure 4-6).
• the working wavelength of the filter is tuned by changing the wavelength of the surfactant, which is controlled by the frequency set by the source 84.
• the double Bragg angle will change, by which beams 76 are deflected by diffraction by the surfactant, and therefore the phase shift between by diffracted beams 77.
• the coherent summation condition phase shift 2 ⁇
• the tunable filter design of FIG. 9 only one filter element based on waveguide 3 and one source 83 of acoustic waves are shown. However, the functionality of the device is greatly expanded if, by analogy with Fig. 6, several successive filtering elements are included in it and additional sources of acoustic waves are used. In this case, the device acquires the property of a multi-channel narrow-band tunable optical filter.
• FIG. 10 A general view of a new filter on coupled strip silicon waveguides (Si wire) is shown in FIG. 10.
• the input signal comes from input 61 to the right waveguide 2 and splits into micro-beams on a set of adiabatic guided couplers (beam dividers) on waveguides 7-12 with different coupling coefficients, which are responsible for filter apodization.
• Each of the micro-beams propagates further in structure and are combined together into an output waveguide 3 using an appropriate set of similar guided couplers on waveguides 13-18.
• the structure has a constant difference in optical length. Thus, at the working wavelength, all micro-beams are summed in phase along the output waveguide and effectively filter at output 62.
• a tapered waveguide 60 (see FIGS. 1, 3-5) must be manufactured, which emits (from the structure) the optical beam entering it, or it must be extended to the right (not shown) channel waveguides, cross it and go further out of the filter (as in figure 2).
• the parameters of all waveguides correspond to typical silicon waveguides with a width of 450 nm and a height of 250 nm, fabricated on silicon-insulator structures.
• the input and output waveguides have curved parts with a small radius of curvature R, as well as different gap widths d of the gap for different communication elements (see Fig. 10), for the implementation of applause.
• R c coefficient dependent FDTD beam dividing
• T c transmission coefficient
• phase shifters for fine and wide tuning.
• the purpose of these phase shifters is to create a controlled linearly varying (from the number of the connecting waveguide) phase delay between the optical micro-beams passing through different paths from the input to the output of the device.
• this filter we carry out filtering due to the thermo-optical effect, namely, by changing the temperature in the corresponding sets of waveguides shown in Fig. 10.
• phase-shifting elements of wide tuning are used, controlled by the scheme of the 2 ⁇ module (manifold module (2 ⁇ ) scheme).
• 2 ⁇ manifold module
• a linearly growing (from the waveguide number) phase shift is formed for all micro-beams, which varies from zero to 2 ⁇ .
• thermo-optical phase-shifting elements located along the X-axis waveguides 36-41 were organized into 4 periodic groups (see Fig. 10). Each of them has its own value of the temperature increase ( ⁇ 0, ⁇ 1, ⁇ 2, ⁇ 3) in channel optical waveguides, which is conveniently determined in units of ⁇ 00, i.e.
• Fig. 146 The results of calculating the spectral characteristics of the optical filter for different combinations of control temperature values in each of the groups of waveguides 36-41 are shown in Fig. 146.
• ⁇ 0 0, and to indicate different values of ⁇ , ⁇ 2 and ⁇ 3, integer numbering was used in the form
• the first value indicates the value of ⁇
• the subsequent digits indicate the values of ⁇ , ⁇ 2 and ⁇ 3 in fractions ⁇ 00.
• the proposed device can be used as a widely tunable optical filter with a small level of internal insertion loss (-1 dB) and high side-lobe suppression (below -26 dB).
• An arbitrary working optical wavelength (within the entire FSR) can be easily adjusted using only 4 control signals, namely, 3 for discrete wavelength tuning with an FSR / 4 step by changing the temperature ⁇ , ⁇ 2 and ⁇ 3 of phase-shifting elements on the connecting waveguides 36-41, as well as by fine continuous tuning within the FSR / 4 range by changing the temperature ⁇ in the phase-shifting fine tuning elements located along the waveguides 2 and 3 of the forming and filtering elements, respectively.
• the total maximum line half-width (FWHM) of an 0.32 mm optical filter using 32 directional couplers with a variable gap d was 1.7 nm.
• FWH depends on the design of the optical filter and the number of beam dividers M s , and in our case it can be estimated as 0.68xFSR / Mc. Scaling of these data for large structures shows that a filter with FWHM less than 0.05 nm can be implemented in a device about 1 cm in size.
• the filter can be tuned within FSR around 37 nm with a moderate temperature change ( ⁇ 100 C 0 ) in four groups of phase-shifting thermo-optical elements .
• FIG. 15 and FIG. 16 describe the expected parameters of a multi-channel tunable filter multiplexer, similar to that shown in FIG. 6, for cases if it were implemented in orthogonal and inclined configurations.
• the beam division coefficient was optimized for different waveguides (see Fig. 15), and it turned out that the dependences of the beam division coefficients Rc 2 , c3, c6 should be different for different waveguides 2, 3-5 and 6, respectively.
• the spectral dependences corresponding to such a distribution of the beam fission coefficients are shown in FIG. 16.
• wavelength tuning due to phase-shifting elements of a thin substring is carried out in a relatively small range (Fig.
• phase shifting elements 16a therefore, for tuning in the range of the entire FSR, it is necessary to additionally apply phase shifting elements of wide adjustment.
• fine-tuning elements can tune the filter wavelength over the entire FSR range (see Fig. 166), with a relatively small change in the temperature of the phase-shifting elements on waveguides 2-6.
• Fig. 17 shows the optimal distribution of the beam division coefficient on waveguides 2 and 3 for a narrow-band filter, for operation with a 25 GHz frequency grid. Its spectral characteristics for different SAW frequencies are shown in Fig. 18. It can be seen that different SAW frequencies correspond to different lengths of the filtered waves (see the upper scale on the graph) having different optical frequencies (see the lower scale on the graph). For clarity, the figure shows the parameters of two filters of different sizes, with 10 times different number of beam dividers, 58 and 580, respectively.
• FIG. 18 A detailed form of the transmission line of a narrow-band acousto-optical filter is shown in Fig. 18. It can be seen that the device has a narrow line width, a high level of suppression of the side lobes and small dimensions (less than 1 cm) at the same time. All these results were obtained in the framework of the ray model and spectral approximation (to describe the wave field in the region of a planar waveguide) according to the algorithm that we developed earlier for the description of acousto-optic filters on multi-reflective elements (A.V. Tsarev, E.A. Kolosovsky "Compact narrow-band tunable acousto-optic filter ", Avtometriya, Volume 42, Ne 6, pp. 93-104 (2006)).
• the optical filter according to the invention simultaneously has a wide tuning range (of the order of 37 nm) and a narrow filter line width (up to 0.05 nm).
• the proposed tunable optical filter can be used in the design of frequency division multiplexing (DWDM) systems used in fiber-optic communication, as well as for creating compact tunable optical radiation spectrometers, for example, when creating remote sensing devices - sensors for the composition of gases, liquids and solids, and also as a part of data reading elements from Bragg fiber sensors.
• DWDM frequency division multiplexing
• the tunable optical filter can be manufactured using well-known technology developed to create integrated optics and microelectronics devices.
• Any transparent solid body for which there is a technology for manufacturing channel and planar optical waveguides with low losses (less than about 1 dB / cm) and effective excitation of acoustic waves can be used as a material for the manufacture of the acousto-optical version of the device.
• Such materials include lithium niobate and tantalate, Ashwu semiconductor heteroepitaxial structures, layered dielectric structures containing a piezoelectric layer for excitation of surfactants, for example, ZnO / Si02 / Si, etc.
• the most promising are devices based on optical waveguides based on lithium niobate, which has good optical, acousto-optical, and electro-optical properties.
• any transparent solid body for which there is a technology for manufacturing channel optical waveguides with low losses can be used. More promising are waveguides with a high refractive index, because channel optical waveguides with a small radius of curvature can be easily implemented in them. Such materials include waveguides based on silicon-insulator structures, as well as AShVu semiconductor heteroepitaxial structures. Moreover, silicon-based waveguides, the so-called silicon wires, are considered the most promising, because they are the most technologically advanced (manufactured by CMOS-compatible technology), cheap and have high thermo-optical properties.
• Waveguides based on semiconductor materials are also interesting in that they can realize a high wavelength switching rate due to a change in the concentration of free charge carriers.
• Devices based on polymer optical waveguides can also be implemented. Their disadvantage is a low refractive index, which makes it difficult to realize small radii of curvature.
• waveguides are cheap, technologically advanced and there is a wide selection of different materials, including those with very good control properties (high values of thermo-optical or electro-optical coefficients).
• the specific choice of design and material of the optical filter depends on the technical task.
• This invention allows to realize different tasks in the most flexible way based on known technologies that have been successfully used in photonics for other types of optical elements, for example, ring resonators and trellis filters at SOI, and / or ring resonators and acousto-optical filters on lithium niobate.

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